1. Field of the Invention
This invention pertains to thermal slab assemblies and, more particularly, to such assemblies which incorporate a plurality of thermoelectric devices, and in which improved air circulation patterns are established across heat sinks for the devices.
2. Review of the Prior Art
Refrigerating thermal slabs, commonly known as cold slabs, have been used for some years by dentists and dental technicians to facilitate the mixing and storage of certain compounds used by such persons in their professional capacities. An exemplary cold slab for dental use is illustrated in U.S. Pat. No. 3,230,723; as set forth below, this invention provides several improvements over the cold slab described in this patent.
Cold slabs are also useful in occupations and businesses other than dentistry. For example, cold slabs may be used by the processors of ophthalmic lenses in connection with the mounting, into appropriate metal holder rings, of unfinished lenses (glass or resin) preparatory to the grinding of the lenses to define the desired prescriptions. An alloy which melts at a very low temperature is injected in molten form into a cavity defined by the metal holder ring in conjunction with the reverse side of the lens element; the alloy solidifies within the cavity and bonds both to the holder ring and to the lens. It is desirable that the alloy solidify as rapidly as possible upon being injected into the cavity so as to transfer a minimal amount of the heat therein to the lens, thereby minimizing distorting thermal stresses in the lens. For this reason, the metal holder rings commonly are chilled to absorb as much heat as possible, as rapidly as possible, from the molten alloy injected into the cavity. Cold slabs may be used to advantage to chill the metal holder rings.
The metal holder rings used in processing ophthalmic lenses should, in practice of the procedure described above, be as cool as possible, but they should not be wet or moist. Accordingly, the temperature to which the holder rings are chilled should be a temperature which is just above the dewpoint in the environment to which the holder rings are exposed. Since the dewpoint will vary from time to time within a manufacturing operation, despite the presence of air-conditioning or the like, it is desirable that the cold slab used to refrigerate or chill the holder ring be adjustable in terms of temperature established and maintained by the slab or chill plate. Existing chill plate assemblies, which are manufactured principally for use in connection with dentistry, do not provide for adjustment for temperature established and maintained in the work surface of the plate, and also are of rather limited capacity in terms of the requirements of a processor of ophthalmic lenses. Also, existing cold slabs, while being satisfactory for dental purposes, are not capable of establishing and maintaining desired temperatures with the accuracy required in the processing of ophthalmic lenses or for many other industrial and domestic purposes. Accordingly, a need exists for a thermal slab which is of increased capacity in terms of its useful work surface, which may be adjustable in terms of the temperature established and maintained in the work surface, and which is of enhanced accuracy in terms of control over such temperature.